1. Field of the Invention
The present invention relates to a head actuator, used in an information recording and reproduction apparatus, for positioning a head on a desired track of an information medium, and a hard disc drive including the same.
2. Description of the Related Art
Recently, recording and reproduction apparatuses using a circular information medium, such as, for example, a magnetic disc apparatus and an optical disc apparatus have been widely used. Among these apparatuses, a magnetic disc apparatus is especially widely used as an external memory apparatus for a personal computer with its characteristic of transferring data at a high speed being utilized.
One small-size magnetic disc apparatus commonly used in recent years uses a magnetic disc having concentric recording tracks and performs information recording and reproduction by positioning a magnetic head on a desired recording track position of the magnetic disc by a swingable head actuator. In order to further improve the recording density, a system for improving the head positioning precision by providing a secondary small head actuator at a tip of the swingable head actuator has been proposed. Several types of small head actuators used for this system have also been proposed.
One exemplary small head actuator is disclosed in Japanese Laid-Open Publication No. 5-47126, which has the following structure. A head supporting spring is formed of two beams. The two beams are connected together at tips thereof, and a head is supported in the vicinity of the connection point. At least one of the beams integrally has a thin film-like displacement element bonded on at least one surface thereof. The displacement element is expandable in accordance with the level of a voltage externally applied. (This type of small head actuator will be referred to as xe2x80x9cconventional example 1xe2x80x9d).
Another exemplary small head actuator is disclosed in Japanese Laid-Open Publication No. 7-224838. In the actuator disclosed in this publication, a piezoelectric element is provided on a surface of a load beam on which a head is to be mounted. (This type of small head actuator will be referred to as xe2x80x9cconventional example 2xe2x80x9d).
Conventional examples 1 and 2 are common in the basic structure. These examples will be described below.
FIG. 15 schematically shows a structure of a conventional head actuator 1200 (corresponding to conventional example 1). As shown in FIG. 15, a head supporting member 50 has a head slider 52 bonded at one end thereof. The head supporting member 50 also has a late-like displacement element 51 bonded to a surface near the center thereof.
As shown in FIG. 15, an area of the head supporting member 50 provided with the displacement element 51 is defined as an area 1201, and areas of the head supporting member 50 where the displacement element 51 is not provided is defined as areas 1202.
In this specification, the term xe2x80x9cneutral facexe2x80x9d is defined to indicate a face which is not expanded or contracted when a beat is bent.
Referring to FIG. 15, a neutral face NB1 of the areas 1202 matches a geometrically central face of the head supporting member 50. In the area 1201, the displacement element 51 is integrally bonded to the head supporting member 50. Therefore, a neutral face NA1 of the area 1201 is inevitably closer to the displacement element 51 than the neutral face NB1. (Hereinafter, a distance D1 between the neutral faces NA1 and NB1 will be referred to as a xe2x80x9cneutral face stepxe2x80x9d. Corresponding distances in the following examples each will also be referred to as the xe2x80x9cneutral face stepxe2x80x9d.) A geometrically central face L1 (also referred to simply as the xe2x80x9ccentral face L1xe2x80x9d) of the displacement element 51 is on the opposite side to the neutral face NB1 with respect to the neutral face NA1. A distance between the central face L1 and the neutral face NA1 is defined as H1.
When a voltage is applied to the displacement element 51, the head supporting member 50 expands or contracts in longitudinal directions relative to the head supporting member 50, and thus the head slider 52 is slightly displaced in a radial direction of a magnetic disc.
In general, two basic performance requirements of a small head actuator are (i) a sufficiently large displacement amount at a lower voltage and (ii) a sufficiently high mechanical resonance frequency so as to realize positioning control in a wide range of band.
The conventional head actuator 1200 has the following two problems. The displacement generated by the expansion and contraction in the longitudinal directions of the head supporting member 50 caused by the voltage application to the displacement element 51 is lost by a flexure of the head supporting member 50, and thus an effective displacement is not obtained. The mechanical resonance frequency mainly relies on the rigidity in flexure directions of the head supporting member 50, and thus it is difficult to obtain a resonance frequency in a wider band range.
First, the problem regarding the displacement will be described.
FIG. 16 shows a static model of the conventional head actuator 1200 (FIG. 15). From the viewpoint of statics, the head actuator 1200 can be represented as a model shown in part (a) of FIG. 16. In part (a) of FIG. 16, the head supporting member 50 is represented by the neutral faces NA1 and NB1. A force provided by the displacement element 51 acts on the head supporting member 50 as an external force.
Now, it is assumed that a voltage is applied to the displacement element 51 in such a direction as to expand the displacement element 51. An expanding force F1 acts outward as shown in part (a) of FIG. 16. Since the central face L1 of the displacement element 51 is on the opposite side to the neutral face NB1 with respect to the neutral face NA1 as described above, a bending moment M1 is generated by the expanding force F1. The bending moment M1 has a magnitude obtained by multiplying the expandable force F1 by the distance H1. On the sheet of FIG. 15, the central face L1 is above the neutral face NA1 by the distance H1. Thus, the bending moment M1 acts in such a direction to cause the neutral face NA1 to project upward on the sheet of FIG. 15. This state is considered to be obtained by the combination of (i) a state of only the expanding force F1 being applied (part (b) of FIG. 16) and (ii) a state of only the bending moment M1 being applied (part (C) of FIG. 16). Considering a length of the area 1201, i.e., the distance between point A and point B, as shown in part (b) of FIG. 16, point A is displaced in such a longitudinal direction as to expand the displacement element 51 by a displacement amount X1. When, as shown in part (c) of FIG. 16, the bending moment M1 is applied in such a direction to cause the neutral face NA1 to project upward, the bending moment M1 generates flexure angles xcex8A and xcex8B at two ends of the displacement element 51. At each of the flexure angles xcex8A and xcex8B, a displacement amount in a longitudinal direction which is obtained by multiplying each of the flexure angles xcex8A and xcex8B by the neutral face step D1 is generated. Thus, points A is displaced in such a longitudinal direction as to contract the displacement element 51 by a displacement amount X2. As is clear from parts (a) and (b) of FIG. 16, the displacement amounts X1 and X2 are in opposite directions. A difference therebetween is a total displacement amount.
When a voltage is applied in such a direction as to contract the displacement element 51, the displacement amounts X1 and X2 are in opposite directions, and a difference therebetween is a total displacement amount. Accordingly, with the structure of the conventional head actuator 1200, the displacement amount X1 generated by the expanding force in one longitudinal direction is lost by the displacement amount X2 generated in the opposite longitudinal direction by the flexure angles. Therefore, a sufficient amount of displacement for positioning the head is not provided.
Next, the problem regarding the mechanical resonance frequency will be described.
FIG. 17 shows a kinetic model of the conventional head actuator 1200 (FIG. 15). The head supporting member 50 can be represented as a model in which an equivalent mass MA1 is concentrated at the center of a beam 1401 (corresponding to the head supporting member 50) having an equivalent flexural rigidity. In FIG. 16, K1 represents an equivalent rigidity in expanding and contracting directions of the head supporting member 50, and MS represents an equivalent mass of a movable body 1402 having the head slider 52 at the center. In this kinetic model, a natural vibration mode is formed by coupling a degree of freedom xcfx86S of the movable body 1402 and a degree of freedom xcfx86Y of the beam 1401 in flexure directions. Namely, an inertial force generated by the vibration of the mass MS in a xcfx86S direction acts on the beam 1401 as a moment M1S due to the neutral face step D1. In the state where the inertial force generated by the vibration of the mass MS of the movable body 1402 in the xcfx86S direction is kinetically balanced with an inertial force generated by the vibration of the equivalent mass MA1 of the beam 1401 in a xcfx86Y direction, the natural vibration mode is formed. The natural frequency of the natural vibration mode is determined by the inertial force generated by the mass MS of the movable body 1402 and an elastic force of the beam 1401 (i.e., the head supporting member 50) in flexure directions. Accordingly, in order to increase the natural frequency, the rigidity of the head supporting member 50 needs to be increased.
However, an increase in the rigidity of the head supporting member 50 increases the resistance against the expanding force of the displacement element 51, which decreases the displacement amount. Conversely, an attempt to guarantee a prescribed displacement amount undesirably results in a decrease in the natural frequency, i.e., mechanical resonance frequency. The displacement amount and the mechanical resonance frequency cannot be satisfied at the same time.
According to one aspect of the invention, a head actuator includes a head slider for carrying a head for recording information to or reproducing information from a recording medium; and a head supporting member for supporting the head slider. The head supporting member includes a substrate and a driving element provided on at least one surface of the substrate for generating an expanding and contracting force in a longitudinal direction in accordance with an external signal, wherein the external signal is applied to the driving element so as to expand or contract the head supporting member in the longitudinal direction and to position the head in a radial direction of the recording medium. The head supporting member includes a first area on which the head slider is provided, a second area on which the driving element is provided, and a third area for connecting the first area and the second area. The driving element has a geometrically central face. The head supporting member has a first neutral face in the second area and a second neutral face in the third area. The second neutral face is on the same side as the geometrically central face with respect to the first neutral face.
In one embodiment of the invention, the first neutral face is closer to the substrate than the geometrically central faces
In one embodiment of the invention, the head supporting member further includes a neutral face displacing section for displacing the second neutral face so as to be on the same side as the geometrically central face with respect to the first neutral face.
In one embodiment of the invention, the neutral face displacing section includes a reinforcing member provided in at least the third area.
In one embodiment of the invention, the first neutral face is an the opposite side to the substrate with respect to the geometrically central face.
In one embodiment of the invention, the head supporting member further includes a geometrically central face displacing section for displacing the first neutral face so as to be on the opposite side to the substrate with respect to the geometrically central face.
In one embodiment of the invention, the geometrically central face displacing section includes a holding member provided on the same side as the substrate with respect to the driving element. The holding member has a function of increasing a rigidity of the head supporting member in a flexure direction and increasing a natural frequency of the head supporting member.
In one embodiment of the invention, the holding member includes a low rigidity layer provided on the driving element and having a smaller longitudinal elastic coefficient than that of the driving element, and a high rigidity layer provided on the low rigidity layer and having a larger longitudinal elastic coefficient than that of the low rigidity layer.
In one embodiment of the invention, the low rigidity layer includes a polyimide resin, and the high rigidity layer includes stainless steel.
In one embodiment of the invention, the head supporting member further includes a first neutral face displacing section for displacing the second neutral face so as to be on the same side as the geometrically central face with respect to the first neutral face.
In one embodiment of the invention, the first neutral face displacing section includes a reinforcing member provided in at least the third area.
In one embodiment of the invention, the reinforcing member is provided on the opposite side to the driving element with respect to the substrate.
In one embodiment of the invention, the driving element has a first elongation rigidity. The substrate has a second elongation rigidity. The first elongation rigidity is larger than the second elongation rigidity.
In one embodiment of the invention, the driving element has a plate-like shape.
In one embodiment of the invention, the driving element includes a piezoelectric element unit including a thin film piezoelectric body and an electrode provided on the thin film piezoelectric body.
In one embodiment of the invention, the driving element includes a first driving element and a second driving element which are supplied with voltages in opposite directions to each other.
In one embodiment of the invention, the substrate includes a first expansion and contraction section having the first driving element provided thereon, a second expansion and contraction section having the second driving element provided thereon, a pivoting section having the head slider provided thereon, a first hinge section for connecting the pivoting section and the first expansion and contraction section, and a second hinge section for connecting the pivoting section and the second expansion and contraction section.
In one embodiment of the invention, the head actuator further includes a load beam for supporting the head supporting member.
According to another aspect of the invention, a head actuator includes a head slider for carrying a head for recording information to or reproducing information from a recording medium; and a head supporting member for supporting the head slider. The head supporting member includes a substrate and a driving element provided on at least one surface of the substrate for generating an expanding and contracting force in a longitudinal direction in accordance with an external signal, wherein the external signal is applied to the driving element so as to expand or contract the head supporting member in the longitudinal direction and to position the head in a radial direction of the recording medium. The head supporting member includes a first area on which the head slider is provided, a second area on which the driving element is provided, and a third area for connecting the first area and the second area. The head supporting member has a first neutral face In the second area and a second neutral face in the third area. The first neutral face and the second neutral face are substantially continuous to each other.
In one embodiment of the invention, the head supporting member includes a continuation section for causing the first neutral face and the second neutral face to be substantially continuous to each other.
In one embodiment of the invention, the continuation section includes an intermediate layer provided between the substrate and the driving element.
In one embodiment of the invention, the continuation section includes a reinforcing member provided in at least the third area.
In one embodiment of the invention, the continuation section includes a line section provided in the vicinity of the driving element.
In one embodiment of the invention, the driving element has a first elongation rigidity. The substrate has a second elongation rigidity. The first elongation rigidity is larger than the second elongation rigidity.
In one embodiment of the invention, the driving element has a plate-like shape.
In one embodiment of the invention, the driving element includes a piezoelectric element unit including a thin film piezoelectric body and an electrode provided on the thin film piezoelectric body.
In one embodiment of the invention, the driving element includes a first driving element and a second driving element which are supplied with voltages in opposite directions to each other.
In one embodiment of the invention, the substrate includes a first expansion and contraction section having the first driving element provided thereon, a second expansion and contraction section having the second driving element provided thereon, a pivoting section having the head slider provided thereon, a first hinge section for connecting the pivoting section and the first expansion and contraction section, and a second hinge section for connecting the pivoting section and the second expansion and contraction section.
In one embodiment of the invention, the head actuator further includes a load beam for supporting the head supporting member.
According to still another aspect of the invention, a hard disc drive includes the above-described head actuator; a motor for rotating the recording medium; a driving section for moving the head actuator across a surf ace of the recording medium in a radial direction of the recording medium so as to allow the head to access a prescribed data track on the recording medium; and a control section for supplying the driving element with an external signal so as to expand or contract the head supporting member in a longitudinal direction and position the head in the radial direction of the recording medium.
Thus, the invention described herein makes possible the advantages of providing a head actuator for offering a larger amount of displacement of a head of an information recording and reproduction apparatus at a lower voltage and also realizing a higher mechanical resonance frequency so as to improve the precision of the head positioning control.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.